Dead cells forward scatter

Fig. 8.25. The use of propidium iodide to monitor cell death. Dead lymphocytes have a less intense forward scatter signal than do live lymphocytes. Cultured Xen-opus spleen lymphocytes courtesy of Jocelyn Ho and John Horton.

The only difficulty in using flow cytometry to monitor cell death is that, as mentioned in Chapter 3, dead cells have different scatter properties than living cells. In particular, because of their perforated outer membrane, they have a lower refractive index than living cells and therefore have forward scatter signals of lower intensity. For this reason, it is important not to use a gate or forward scatter threshold when analyzing a population for the proportion of dead and live cells. Any forward versus side scatter gate drawn around normal lymphocytes, for example, will always show most if not all of the cells... 

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